Displays are created by arranging thin film transistor (TFT) in a matrix which acts as a controller to each pixel. The most commonly available substrate material is glass in the display fabrication process. However, glass is not desirable due to its heaviness, fragility and a relatively high cost. In addition, with the increasing demand for achieving lighter and thinner displays, more efforts have been made for the development to reduce thickness of glass substrates. However, since displays must be handled with extreme care to avoid breakage, the fabrication process becomes complicated and the manufacturing costs is increasing due to low productivity (Appl. Phys., A, 72, 699(2001)).
Recently, plastic has been developed to replace glass as a starting material for display fabrication. Plastic substrates are advantageous in that they are light-weighted and rugged but have also high impact resistance, flexibility, and ability for roll to roll manufacturing process so that plastics may be more widely used in place of glass on the display industry. With requirements of color clarity, high dimensional stability, low moisture absorption and the like for plastic substrates used for displays, polyethylene terephthalate (PET), polyethersulfone (PES), polycarbonate (PC), and cyclic olefin polymer have been used. With the aforementioned excellent characteristics in use for plastic substrates on displays, however, chemical resistance is also required because they are exposed to solvents for various chemical treatments during the manufacturing process. Most commercially available plastic materials are PC, PET, PES and the like but there is still significant room for improvement on chemical resistance of resins.
In order to improve the chemical resistance of resins, methods such as modification of polymer structure, surface coating and introduction of cross-likable groups have been used. A typical method for forming cured film or coating layer is to directly coat on plastic substrate with heat curable resin solution or UV curable resin solution or form a thin film having a thickness of 1-15 μm as a buffer layer. Japan Unexamined Patent Publication No. 2003-191370 discloses a method for coating thermo-setting polymer on a plastic substrate and a method for forming crosslinkage by polymerization of monomers containing acryloyl or methacryloyl groups. Japan Unexamined Patent Publication No. 2002-60506 discloses a method for coating alicyclic acrylate polymer on the surface of the plastic substrate and curing with UV rights. Further, Korea Unexamined Patent Publication No. 2001-76642 discloses that acrylate functional groups are UV-treated by dispersion of silica particles and silicone-based surfactant to enhance chemical resistance and rigidity.
However, conventional methods for coating resins on the substrate use compounds which have a different composition for coating materials from those of the substrate so that it causes separation between layers due to difference in coefficient of thermal expansion during the manufacturing process of display modules, thus resulting in distortion and haze.
Accordingly, the inventors of the present invention have noticed that even if conventional polyether resins such as polysulfone, polyethersulfone, and polycarbonate resins have excellent optical transmission, there is still limitation to use those resins for display substrates due to their poor chemical resistance and thus have intensively studied to develop polyether resins with excellent chemical resistance.